Datasheet

TS5205
Taiwan Semiconductor
Document Number: DS_P0000197 5 Version: I15
APPLICATION INFORMATION (CONTINUE)
Reference Bypass Capacitor
Bypass is connected to the internal voltage reference. A 470pF capacitor (C
BYPASS
) connected from Bypass to
Ground quiets this reference, providing a significant reduction in output noise. C
BYPASS
reduces the regulator
phase margin; when using C
BYPASS
, output capacitors of 2.2µF or greater are generally required to maintain
stability. The star up speed of the TS5205 is inversely proportional to the size of the reference bypass capacitor.
Applications requiring a slow ramp up of output voltage should consider larger values of C
BYPASS
. Likewise, if
rapid turn on is necessary, consider omitting C
BYPASS
. If output noise is not a major concern, omitted C
BYPASS
and
leave Bypass open.
Adjustable Regulator Design
The adjustable regulator versions can be adjusted to a specific output voltage by using two external resistors to
programming the output voltage anywhere between 1.25V and the 8V maximum operating rating of the family.
Two resistors are used. Resistors can be quite large up to 470kΩ, because of the very high input impedance and
low bias current of the sense comparator, the resistor values are calculated by:
A capacitor from Adjust to Ground provides greatly improved noise performance.
Dual Supply Operation
When used in dual supply systems where the regulator load is returned to a negative supply, the output voltage
must be diode clamped to ground.
Thermal Characteristics
TS5205 series is designed to provide 150mA (5V version) of continuous current in a very small package.
Maximum power dissipation can be calculated based on the output current and the voltage drop across the part.
To determine the maximum power dissipation of the package, use the junction-ambient thermal resistance of the
device and the following basic equation:
P
D(MAX)
= [ T
J(MAX)
– T
A
] /Θ
JA
T
J(MAX)
is the maximum junction temperature of the die(125
o
C), and Ta is the ambient operating temperature. Θ
JA
is layout dependent, the actual power dissipation of the regulator circuit can be determined using the equation:
P
D
= (V
IN
– V
OUT
) * I
OUT
+ V
IN
* I
GND
Substituting P
D(MAX)
for P
D
and solving for the operating conditions that are critical to the application will give the
maximum operating conditions for the regulator circuit. For example, when operating the TS5205CX33 at room
temperature with a minimum footprint layout, the maximum input voltage for a set output current can be
determined as follows:
P
D(MAX)
= (125
o
C – 25
o
C) / 220
o
C/W
P
D(MAX)
= 455mW
C
OUT
2.2µF
on
off
EN
R1
R2
V
IN
V
OUT
C
BYP
470pF
TS5205CX5
Adjustable Version: V
OUT
= 1.24 (1+R2/R1)
(Adjustable output range up to 8V)